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Hubble in double trouble

In safe mode as NASA probes two systems 'anomalies'

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The reactivation of the Hubble space telescope has been suspended while NASA probes a couple of systems 'anomalies' following the boot-up of its back-up computer system.

The venerable eye in the sky was last month blinded by the failure of the Control Unit/Science Data Formatter (CU/SDF) in its operational Side A Science Instrument Command and Data Handling unit (SIC&DH), which packets data from the 'scope's five main instruments for transmission back to Earth.

NASA responded by firing up the redundant Side B system, and hoped to have Hubble back in full science mode last Friday. However, the agency now reports that while instrument reconfiguration "proceeded nominally" and the Wide Field Planetary Camera 2, Near Infrared Camera and Multi Object Spectrometer were successfully commanded from safe to operate modes, things didn't go quite so smoothly with the Advanced Camera for Surveys (ACS).

NASA explains that on 16 October "an anomaly occurred during the last steps of the commanding to the Advanced Camera for Surveys". The report elaborates: "At 1:40 pm [Eastern Time], when the low voltage power supply to the ACS Solar Blind Channel was commanded on, software running in a microprocessor in ACS detected an incorrect voltage level in the Solar Blind Channel and suspended ACS.

"Then at 5:14 pm, the Hubble spacecraft computer sensed the loss of a 'keep alive' signal from the NASA Standard Spacecraft Computer in the SIC&DH and correctly responded by safing the NSSC-I and the science instruments. It is not yet known if these two events were related."

NASA concludes: "The investigation into both anomalies is underway. All data has been collected and is being analyzed. The science instruments will remain in safe mode until the NSSC-I issue is resolved. All other subsystems on the spacecraft are performing nominally and astrometry observations continue." ®